One other observation. There is a striking plurality of newbs purporting to be affected by this... which, to some extent, might suggest that the real nature of this attack might be some kind of weird social engineering trick either to make MtGox look bad or create Bitcoin FUD....
I don't know if Mt. Gox has been comprimised or not and I'm not ruling out your idea, but the fact that mostly newbs are posting here could be because (a) this is the only place they can post, and (b) they didn't register here until they had a reason to post, i.e. a problem.